Process of extraction of hemicellulose from corn fiber

Abstract

A process of separating one or more components of corn fiber that comprises contacting the corn fiber with an extraction fluid that comprises at least one weak acid, increasing the temperature of the resulting mixture of fiber and fluid to solubilize hemicellulose of the corn fiber into the fluid, cooling the mixture, and separating the cooled extraction mixture into a soluble fraction comprising dissolved hemicellulose and an insoluble fraction comprising cellulose.

The invention claimed is: 
     
       1. A process of separating one or more components of destarched corn fiber, the process comprising:
 (a) contacting the destarched corn fiber, which comprises a matrix that comprises hemicellulose, cellulose and lignin, with an aqueous extraction fluid that comprises at least one weak acid at a total concentration of weak acid(s) in the range of about 0.01 M to about 1 M to form an extraction mixture; 
 (b) solubilizing hemicellulose of the destarched corn fiber by controlling the temperature of the extraction mixture so that the extraction fluid is sufficiently acidic to break linkages between hemicellulose and lignin via hydrolysis, T SOL , thereby dissolving the solubilized hemicellulose into the extraction fluid; 
 (c) quenching hydrolysis by controlling the temperature of the extraction mixture so that the extraction fluid is not sufficiently acidic to substantially depolymerize the dissolved hemicellulose, T QUENCH ; and 
 (d) separating the extraction mixture into a soluble fraction comprising dissolved hemicellulose and an insoluble fraction comprising cellulose and lignin, 
 wherein
 the dissolved hemicellulose of the soluble fraction is at an amount that is in the range of 30 to 75% by weight of the de-starched corn fiber and the cellulose of the insoluble fraction is at an amount that is in the range of 15 to 30% by weight of the de-starched corn fiber; 
 at least 30% by weight of the dissolved hemicellulose has a degree of polymerization of at least 11; 
 no more than 10% by weight of the dissolved hemicellulose has a degree of polymerization in the range of 3 to 10; and 
 no more than 60% by weight of the dissolved hemicellulose has a degree of polymerization in the range of 1-2. 
 
 
     
     
       2. The process of  claim 1  further comprising treating the soluble fraction to separate the dissolved hemicellulose from the extraction fluid. 
     
     
       3. The process of  claim 1 , wherein the at least one weak acid is selected from the group consisting of citric acid, lactic acid, malic acid, acetic acid, fumaric acid, formic acid, oxalic acid, and combinations thereof. 
     
     
       4. The process of  claim 1 , wherein the extraction mixture has a weight ratio of corn fiber to extraction fluid that is in the range of about 1:100 to about 60:100. 
     
     
       5. The process of  claim 4 , wherein T SOL  is in the range of about 50° C. to about 350° C. and the extraction mixture is at T SOL  for a duration, t SOL , that is in the range of about 1 minute to about 200 minutes, T QUENCH  is in the range of about 5° C. to about 40° C., and the average rate of change from T SOL  to T QUENCH  during the quenching is in the range of about 0.1° C./s to about 5° C./s. 
     
     
       6. The process of  claim 5 , wherein the dissolved hemicellulose of the soluble fraction comprises (i) monosaccharides and disaccharides at a total amount that is in the range of about 20 to about 75% by weight of the dissolved hemicellulose, (ii) oligosaccharides at a total amount that is less than about 10% by weight of the dissolved hemicellulose, and (iii) polysaccharides at a total amount that is in the range of about 30 to about 70% by weight of the dissolved hemicellulose. 
     
     
       7. The process of  claim 1 , wherein the extraction mixture has a weight ratio of corn fiber to extraction fluid that is in the range of about 3:100 to about 20:100. 
     
     
       8. The process of  claim 7 , wherein T SOL  is in the range of about 120° C. to about 150° C. and the extraction mixture is at T SOL  for a duration, t SOL , that is in the range of about 2 minute to about 10 minutes, T QUENCH  is in the range of about 10° C. to about 30° C., and the average rate of change from T SOL  to T QUENCH  during the quenching is in the range of about 0.5° C./s to about 1° C./s. 
     
     
       9. The process of  claim 8 , wherein the corn fiber is de-starched corn fiber; the dissolved hemicellulose of the soluble fraction is at an amount that is in the range of about 50 to about 60% by weight of the de-starched corn fiber and the cellulose of the insoluble fraction is at an amount that is in the range of about 20 to about 30% by weight of the de-starched corn fiber; and the dissolved hemicellulose of the soluble fraction comprises (i) monosaccharides and disaccharides at a total amount that is in the range of about 30 to about 40% by weight of the dissolved hemicellulose, (ii) oligosaccharides at a total amount that is less than about 5% by weight of the dissolved hemicellulose, and (iii) polysaccharides at a total amount that is in the range of about 55 to about 70% by weight of the dissolved hemicellulose. 
     
     
       10. A process of  claim 1 , wherein at least 40% by weight of the dissolved hemicellulose has a degree of polymerization of at least 3. 
     
     
       11. The process of  claim 10 , wherein: the at least one weak acid is selected from the group consisting of citric acid, lactic acid, malic acid, acetic acid, fumaric acid, formic acid, oxalic acid, and combinations thereof; the extraction fluid has a total concentration of weak carboxylic acids(s) that is in the range of about 0.001 M to about 10 M; the extraction mixture has a weight ratio of de-starched corn fiber to extraction fluid that is in the range of about 1:100 to about 60:100; and the controlling the temperature of the extraction mixture comprises keeping it within a range that is from about 50° C. to about 350° C. for a duration that is in the range of about 1 minute to about 200 minutes and then quenching it to a temperature below than said range. 
     
     
       12. The process of  claim 10  further comprising separating the extraction mixture into a soluble fraction comprising dissolved hemicellulose and an insoluble fraction comprising cellulose and lignin from the de-starched corn fiber. 
     
     
       13. The process of  claim 12  further comprising separating the dissolved hemicellulose from the extraction fluid. 
     
     
       14. The process according to  claim 1 , wherein the weak acid has a pK a  greater than 0. 
     
     
       15. The process according to  claim 1 , wherein the extraction fluid is a mixture of water and the weak acid. 
     
     
       16. The process according to  claim 1 , wherein the weak acid is citric acid. 
     
     
       17. The process according to  claim 1 , wherein the weak acid has a pK a  of at least 2. 
     
     
       18. The process of  claim 17 , wherein T SOL  is in the range of about 120° C. to about 150° C. and the extraction mixture is at T SOL  for a duration, t SOL , that is in the range of about 2 minute to about 10 minutes, T QUENCH  is in the range of about 10° C. to about 30° C., and the average rate of change from T SOL  to T QUENCH  during the quenching is in the range of about 0.5° C./s to about 1° C./s. 
     
     
       19. The process of  claim 18 , wherein the extraction mixture does not comprise any strong acids. 
     
     
       20. The process of  claim 17 , wherein the extraction mixture does not comprise any strong acids. 
     
     
       21. The process of  claim 1 , wherein the weak acid has a pK a  of at least 4. 
     
     
       22. The process of  claim 21 , wherein T SOL  is in the range of about 120° C. to about 150° C. and the extraction mixture is at T SOL  for a duration, t SOL , that is in the range of about 2 minute to about 10 minutes, T QUENCH  is in the range of about 10° C. to about 30° C., and the average rate of change from T SOL  to T QUENCH  during the quenching is in the range of about 0.5° C./s to about 1° C./s. 
     
     
       23. A process of separating one or more components of de-starched corn fiber, the process comprising solubilizing and dissolving hemicellulose from the de-starched corn fiber into an extraction fluid of an extraction mixture, which comprises about 6.5 parts by weight of de-starched corn fiber and about 100 parts by weight of the extraction fluid, wherein the extraction fluid comprises citric acid at a concentration in the range of about 0.01 M to about 0.05 M by controlling the temperature of the extraction mixture so that it is in the range of about 120° C. to about 150° C. for a duration in the range of about 2 minutes to about 10 minutes and then quenching it to a temperature below said range so that (a) the amount of dissolved hemicellulose is in the range of about 50 to about 60% by weight of the de-starched corn fiber, (b) the dissolved hemicellulose comprises (i) monosaccharides and disaccharides at a total amount that is in the range of about 30 to about 40% by weight of the dissolved hemicellulose, (ii) oligosaccharides at a total amount that is less than about 5% by weight of the dissolved hemicellulose, and (iii) polysaccharides at a total amount that is in the range of about 55 to about 70% by weight of the dissolved hemicellulose. 
     
     
       24. A process of separating one or more components of corn fiber, the process comprising:
 (a) contacting the corn fiber, which comprises a matrix that comprises hemicellulose, cellulose and lignin, with an extraction fluid that comprises at least one weak acid to form an extraction mixture, the extraction mixture having a total concentration of weak acid(s) that is in the range of about 0.01 M to about 1 M, the extraction mixture having a weight ratio of corn fiber to extraction fluid that is in the range of about 3:100 to about 20:100; 
 (b) solubilizing hemicellulose of the corn fiber by controlling the temperature of the extraction mixture so that the extraction fluid is sufficiently acidic to break linkages between hemicellulose and lignin via hydrolysis, T SOL , thereby dissolving the solubilized hemicellulose into the extraction fluid; 
 (c) quenching hydrolysis by controlling the temperature of the extraction mixture so that the extraction fluid is not sufficiently acidic to substantially depolymerize the dissolved hemicellulose, T QUENCH , and 
 (d) separating the extraction mixture into a soluble fraction comprising dissolved hemicellulose and an insoluble fraction comprising cellulose, 
 
       wherein T SOL  is in the range of about 120° C. to about 150° C. and the extraction mixture is at T SOL  for a duration, t SOL , that is in the range of about 2 minute to about 10 minutes, T QUENCH  is in the range of about 10° C. to about 30° C., and the average rate of change from T SOL  to T QUENCH  during the quenching is in the range of about 0.5° C./s to about 1° C./s. 
     
     
       25. The process of  claim 24 , wherein the corn fiber is de-starched corn fiber; the dissolved hemicellulose of the soluble fraction is at an amount that is in the range of about 50 to about 60% by weight of the de-starched corn fiber and the cellulose of the insoluble fraction is at an amount that is in the range of about 20 to about 30% by weight of the de-starched corn fiber; and the dissolved hemicellulose of the soluble fraction comprises (i) monosaccharides and disaccharides at a total amount that is in the range of about 30 to about 40% by weight of the dissolved hemicellulose, (ii) oligosaccharides at a total amount that is less than about 5% by weight of the dissolved hemicellulose, and (iii) polysaccharides at a total amount that is in the range of about 55 to about 70% by weight of the dissolved hemicellulose.